Fractures of limb bones have been treated with internal fixation devices, such as plates lying on the surface of a bone, nails running inside the medullary canal of a fractured bone, and/or screws affixing both ends of a fractured bone together. These internal fixation devices may provide reasonable structural rigidity and/or stability to the fractured bone without compromising some of the strain desired to stimulate bone cells.
An intramedullary fixation method is a traditional procedure for treating long bone fractures, affixing the bone fracture using intramedullary nails, without disturbing the periosteum of the bone. Such a method may be accomplished in a closed manner, and the fractured bone may be functionally used (including weight bearing) during healing. The surgical approach for insertion of intramedullary nails varies slightly for each bone and is well described in the orthopedic literature.
Some of the problems associated with conventional intramedullary fixation methods include lack of rotation stability, collapse of the fracture site in some fracture types, and/or undesired backup of nails. Furthermore, although the actual shape of the bone typically includes some degree of curvature, the intramedullary nails used to mend the fractured bone are generally straight. Still further, intramedullary fixation methods may introduce interlocking screws across the nail, creating some disadvantages. Specifically, conventional intramedullary fixation nails for long bones may include a rigid structure (hollow or full), that may be locked at their extremes by the addition of screws transversally applied through the bone walls and the nail itself. This additional step generally makes the operation longer and more complicated, and may require additional skin incisions and/or longer use of an image intensifier (X-ray). Furthermore, undesired gaps between the bone ends may originate from the screws, which are permanent unless removed in a new operation. Also, the resultant structure in certain situations may be too stiff and may lack desired elasticity. In contaminated fractures, metallic intramedullary nails may propagate contamination through the entire canal, despite attempts at cleaning the fracture site, which may lead to bone infection.
Recent developments in the intramedullary fixation approach have attempted to address some of these problems. For example, PCT Publication No. WO 98/38918 to Beyar suggests three structural designs: (1) a solid metal sheet that expands in the medullary canal; (2) a meshwork structure consisting of ribs circumferentially connected at the tips; and (3) a balloon structure that is inflated once inserted into the medullary canal. The first two structures, however, may not provide firm support within the metaphysis of the bone. Specifically, these structures are unable to expand at their ends, because the total expansion of the structures is limited by the circumference of the diaphyseal segment of the medullary canal. The balloon structure also has limited utility because, when inflated, it may disrupt blood supply of the bone and prevent regeneration or recovery, and/or may not be adjustable to changes in the shape of the medullary canal, because of its set volume once inserted and inflated.
U.S. Pat. No. 5,281,225 to Vicenzi discloses a structure that includes a multitude of elastically deformable stems connected together by a stub. When inserted in the medullary canal of a fractured bone, the distal tips of the stems expand outward into the end of the medullary canal to anchor the Vicenzi structure within the bone. This device, however, is a passive device, expanding automatically upon deployment, and may not be controllably expanded. Additionally, the Vicenzi structure is not expanded within the medullary canal and, thus, does not provide multiple points of contact with the wall of the medullary canal. As a result, the Vicenzi structure may not ensure structural stability along the transversal and rotational planes of the fractured bone.
Accordingly, intramedullary devices that provide and/or ensure stability to a fractured bone would be considered useful.